Satellite positioning systems (SPSs), such as the global positioning system (GPS), have enabled navigation services for mobile handsets in outdoor environments. Likewise, particular techniques for obtaining estimates of positions of mobile devices in indoor environments may enable enhanced location based services in particular indoor venues such as residential, governmental or commercial venues. For example, a range between a mobile device and a transceiver positioned at a fixed location may be measured based, at least in part, on a measurement of a received signal strength (RSSI) or a round trip time (RTT) measured between transmission of a first message from a first device to a second device and receipt of a second message at the first device transmitted in response to the first message.
Use of RTT and RSSI measurements for ranging is very inaccurate in band limited systems such as Bluetooth. With RTT based ranging in particular, this is in part because narrow bandwidth may involve a blurring of multipath components. In wireless telecommunications, multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Inaccuracy occurs also because accuracy typically depends on determination of precise times of reception and departure in the presence of drifting clocks and complex receive chains. Therefore, measuring ranges between devices using RTT based measurements is complex and may suffer inaccuracies in the presence of clock drift and multipath.
Accordingly, there is a need for systems, apparatus, and methods that improve conventional approaches including the methods, system and apparatus provided hereby.